Re-land: base: Introduce an explicit call for reducing emulated discardable memory usage.

base/memory/discardable_memory_emulated.cc

Index: base/memory/discardable_memory_emulated.cc
diff --git a/base/memory/discardable_memory_emulated.cc b/base/memory/discardable_memory_emulated.cc
index 340a181834ad3dbed5058cd419467f05013bc6f8..ca0026a2dff81fdff9e43db47ee568492ffd6fe3 100644
--- a/base/memory/discardable_memory_emulated.cc
+++ b/base/memory/discardable_memory_emulated.cc
@@ -45,18 +45,21 @@ DiscardableMemoryEmulated::~DiscardableMemoryEmulated() {
 }
 
 // static
-void DiscardableMemoryEmulated::RegisterMemoryPressureListeners() {
-  g_shared_state.Pointer()->manager.RegisterMemoryPressureListener();
+bool DiscardableMemoryEmulated::ReduceMemoryUsage() {
+  return g_shared_state.Pointer()->manager.ReduceMemoryUsage();
 }
 
 // static
-void DiscardableMemoryEmulated::UnregisterMemoryPressureListeners() {
-  g_shared_state.Pointer()->manager.UnregisterMemoryPressureListener();
+void DiscardableMemoryEmulated::SetModeratePressureLimit(size_t bytes) {
+  g_shared_state.Pointer()
+      ->manager.SetBytesToKeepUnderModeratePressure(bytes);
 }
 
 // static
-bool DiscardableMemoryEmulated::ReduceMemoryUsage() {
-  return g_shared_state.Pointer()->manager.ReduceMemoryUsage();
+void
+DiscardableMemoryEmulated::ReduceMemoryUsageUntilWithinModeratePressureLimit() {
+  g_shared_state.Pointer()
+      ->manager.ReduceMemoryUsageUntilWithinModeratePressureLimit();
 }
 
 // static